This application claims priority of German Application No. 198 52 948.1, filed Nov. 12, 1998 and International Application No. PCT/EP99/05888, filed Aug. 11, 1999, the complete disclosure of which is hereby incorporated by reference.
a) Field of the Invention
The invention is directed to a handpiece for cosmetic treatment of skin surfaces, by which a laser beam is directed to a selected skin area which is subjected to the action of the laser beam. The invention is further directed to a method for cosmetic treatment of skin surfaces while operating a handpiece of the type mentioned above.
b) Description of the Related Art
Lasers are currently used the world over for cosmetic treatment of the skin, primarily of vascular and pigmented lesions, e.g., for removal of port-wine stains and tattoos, for skin resurfacing and also for hair removal. Usually, short laser pulses with a pulse duration in the nanosecond to millisecond range are introduced into the tissue for this purpose. Treatments of this kind serve primarily to improve the quality of life of the patient and are generally of a cosmetic nature.
The equipment for carrying out such treatments essentially comprises a laser radiation source and a handpiece which is used for directing the beam emitted by the laser radiation source onto the skin area to be treated.
In order to achieve a lightweight construction of the handpiece and thus to enable the freest possible handling of the handpiece, the laser radiation source and handpiece are constructed as separate subassemblies, and the transmission of laser radiation from the radiation source to the handpiece is carried out by means of a movable beam guidance device. The beam guidance unit can be formed of a plurality of rigid transmission members interconnected by joints or may also be constructed as a flexible fiber optic system or in some other way.
The handpiece has an in-coupling element at the transition from the beam guidance unit and an emission surface for the laser beam is provided at the end of the handpiece to be directed to the skin. Often, there is a spacer which fixes the working plane and accordingly ensures that the cross section and intensity of the applied laser beam in the working plane correspond to the selected parameters.
For many dermatological applications, it is advantageous to cool the outer skin layers in order to prevent laser radiation damage. Various methods and devices are known for this purpose.
For example, it is common to apply cooling gel to the surface to be treated or the surface to be treated is cooled by a spray. However, it is difficult to influence the temperature on the skin and in the layers located immediately below it in such a way that the desired treatment effect is achieved on the one hand and laser radiation damage to the epidermis is extensively prevented on the other hand. A further disadvantage consists in that a local uniform cooling is not guaranteed.
U.S. Pat. No. 5,057,104 describes a method and a device for treating cutaneous vascular lesions in which the laser beam is guided by a stationary cooling container communicating with the skin segment to be treated. In this way, heat is removed from the skin area during treatment.
U.S. Pat. No. 5,735,844 discloses a device for hair removal in which an optically transparent lens through which the laser beam is directed onto the skin area to be treated is brought into contact with a cooling unit as well as with the skin. In so doing, the lens also removes heat during the treatment of the skin area in question, as was described above.
In the devices mentioned above, the large space requirement caused by the dimensions of the cooling means placed on the skin has proved disadvantageous. This constitutes a hindrance when treating small surfaces. Further, the heat conductivity of the available materials which are transparent for laser radiation is comparatively poor so that fast, optimal cooling cannot be achieved.
Another substantial disadvantage consists in that when positioning the outlet optics for the laser beam and the cooling device it is initially necessary to wait before irradiating with laser energy until the skin site to be treated has cooled optimally. This is particularly disadvantageous when treating a larger skin surface on which the laser radiation must be introduced in several adjacent skin areas. The treatment period is relatively long due to the fact that a dwell or holding time is required for cooling for each of these skin areas first and the laser irradiation can take place only then.
Also, post-treatment of the affected skin portions by means of temperature control is impossible with the known handpieces.
Based on this prior art, it is the primary object of the invention to further develop a handpiece for cosmetic treatment of skin areas by means of laser radiation in such a way that a more efficient treatment is ensured while protecting the skin as far as possible.
According to the invention, a handpiece of the type described above is outfitted with a device for moderating the temperature of the selected skin surface before and/or after its treatment. Accordingly, it is possible for a skin surface to be cooled or heated, as required, immediately before treatment with laser radiation and also, if required, to subject it to post-treatment by supplying or removing heat.
In a handpiece by which the laser beam is directed successively to individual skin areas corresponding to the laser beam cross section and covering the selected skin surface in its entirety, there is at least one temperature-moderated contact surface laterally adjacent to the exiting laser beam. According to the invention, the distance between the laser beam and a contact surface of the type mentioned above is dimensioned in such a way that a first skin area on which the laser beam was previously directed and on which the laser beam has just acted is in contact with the contact surface at the same time that the laser beam is directed to a second skin area. Alternatively or in addition, there can be another contact surface whose distance from the laser beam is so dimensioned that it is in contact with a third skin area on which the laser beam is to act in the next step (while the laser beam is still simultaneously directed to the second skin area and the first skin area is still in contact with the first contact surface).
Similarly, additional contact locations can be provided at the handpiece and, while the laser beam is directed to and acts on the second skin area, these other contact locations are in contact with other previously treated skin areas and/or with other skin areas to be treated subsequently by means of moderating temperature.
In other words, the contact surfaces are positioned at the handpiece in relation to the laser beam in such a way that while the laser beam acts upon a skin area, at least one other skin area on which the laser beam had acted previously (before moving the handpiece) and/or on which the laser beam is to act subsequently (after the handpiece is moved) is in contact with a contact surface. In this way, the temperature of the individual skin areas is moderated in immediate preparation for the laser beam action and/or for purposes of post-treatment. The handpiece can therefore be advanced progressively from one skin area to another without delay.
In construction variants, the dimensions of the contact surface may be smaller or larger than the dimensions of the laser beam cross section. In this way, it is possible, for example, to moderate the temperature of a larger surface portion before treatment, so that only surface portions whose temperature has already been moderated are subjected to the action of the laser beam and safety is increased. Moderating the temperature of a surface that is smaller in comparison to the laser beam cross section can serve for a gentler treatment of certain skin areas.
According to the invention, the at least one contact surface is connected with a cooling unit and/or heating unit in a heat-conducting manner. Preferably, a cooling unit is provided. This cooling unit may be constructed, for example, as a Peltier element whose cool side communicates in a heat-conducting manner with the contact surface, the heat removed from the skin area being carried away from its warm side via a medium which circulates in a cooling circuit.
Alternatively, it is also possible that the contact surface is made to communicate in a heat-conducting manner with an expanding, and therefore cooling, gas, e.g., nitrogen or carbon dioxide, while this contact surface rests on the skin area whose temperature is to be moderated beforehand.
In a particularly preferred construction, a temperature sensor is provided at the handpiece and communicates with the contact surface and/or with the skin area which is selected for treatment and whose temperature is to be moderated. It is determined by means of this temperature sensor whether or not the skin area has reached the temperature that is required for treatment and that is a precondition for successful treatment. The output signal of the temperature sensor can be used as a switch-on signal or control signal for the cooling and/or heating unit. In this way, it is possible to further increase or reduce the temperature of the selected skin area, as needed.
In another construction, the laser beam cross section is surrounded by an annular surface which rests on the skin area selected for treatment. By means of this annular surface, the skin area can be exposed to a pressure which favors successful treatment because the thickness of the epidermis is reduced by the area pressure between the annular surface and the skin, so that the laser energy penetrates into the skin more effectively.
In an additional construction, instead of the annular surface, the handpiece is provided with slide rails or guide rollers which facilitate manual guiding in a straight line over the skin surface. This is particularly advantageous when the laser radiation source is not switched on and off when moving from one skin area to the next, but rather the switched on laser beam is guided in a continuous, sliding manner over the skin surface. Also, the required distance of the emission surface from the skin is always ensured at the same time by means of such glide rails.
The glide rails can advantageously be constructed as filter glass disks which protect the operator from the laser radiation at the same time.
The handpiece according to the invention can also be constructed in such a way that at least one optical element with a surface which is structured in the micrometer range and is accordingly micro-optically active is provided inside the handpiece following the exit face of the beam guidance device.
This surface can have a diffractively acting structure whose width is in the order of magnitude of the wavelength of the laser beam utilized for treatment. A structure of this kind is, for example, a varying height profile with stripe-shaped, cross-shaped, funnel-shaped and/or otherwise shaped raised portions, an index of refraction varying within the above-mentioned structure width and/or varying absorption coefficients. Elements outfitted with surfaces of this type are described, for example, in Naumann, Schrxc3x6der, xe2x80x9cBaulemente der Optik [Optical Components]xe2x80x9d, Carl Hanser Verlag, Munich, Vienna, 6th edition, page 584.
By means of this microstructured surface, the energy distribution within the beam cross section is made uniform to the edge areas when the laser beam passes through this surface, i.e., a radiation intensity which is uniform over the cross section is present in the beam path following this surface over the entire beam cross section.
In an alternate construction, instead of the diffractive structure, the surface has a refractively acting structure formed, for example, of spherical, aspherical, cylindrical and/or elliptic lenses, wherein each of the lenses has a dimension vertical to the beam direction of 10 m to 1000 m. These lenses can be arranged hexagonally and/or orthogonally on the surface as an array. They can be concave dispersive lenses or convex collective lenses; concave and convex lenses can also be arranged adjacent to one another on the surface. Randomly oriented concave cutouts, notches arranged in a circle or extending helically or intersecting gratings are also conceivable.
Preferred dimensions for the refractive structures are diameters of 0.35 mm and depths of 0.005 mm. The ratio of depth to diameter should not exceed 0.5. With respect to lens structures, this ratio should be greater than 0.02 and, in particularly preferred constructions, in the range of 0.1 to 0.3.
When the laser beam passes the surface, the radiation is divided into a plurality of partial beams through the micro-optically active structure elements (lenses or height profiles), wherein the quantity of partial beams depends on the quantity of structure elements present on the surface. The finer the micro-optically active structure, the more uniform and homogeneous the distribution of the beam intensity over the entire cross section of the laser beam after passing through the described surface. In other words, when passing through the microstructured surface, an uneven energy distribution within the beam cross section is transformed into a uniform energy distribution to the edge areas of the beam cross section.
This homogenization is particularly necessary and advantageous when using a ruby laser as radiation source because, as is well known, its radiation has a highly inhomogeneous intensity distribution in cross section. In addition, the intensity distribution in the ruby laser beam is not constant, but changes from spot to spot, so that when the ruby laser is used for hair removal without the device proposed according to the invention burning can easily result.
According to the invention, not only is the intended homogenization of the intensity within the beam cross section achieved with the microstructured surface but, depending on the construction of the individual structure elements, the direction of the individual partial beams can also be influenced insofar as this is intended and desired. This means that a laser beam exiting from a fiber, e.g., with circular cross section, can be changed into a laser beam with a square, rectangular, hexagonal or otherwise shaped beam cross section by means of deliberate predetermined shaping of the individual structure elements.
This means that when square, rectangular or hexagonal beam cross sections are directed onto the skin area to be treated, the individual spots can be placed adjacent to one another without overlapping while also preventing missed untreated locations. Elimination of overlap prevents an excessive introduction of energy and elimination of untreated missed locations prevents insufficient introduction of energy, so that the treatment results are significantly improved.
The reshaping of the beam cross section is achieved in that the structure elements on the microstructured surface are selected, shaped and positioned in such a way that the partial beams are given a direction within the laser beam cross section aiming at a desired outer contour of the cross section. Accordingly, the partial beams no longer fill up a circular beam cross section, but, for example, uniformly fill up a square cross section (the circle segments are cut out).
Accordingly, compared with the prior art, the handpiece according to the invention is characterized by an intensity of the laser beam at the emission surface that is homogenized over the entire cross section and, moreover, by an adapted cross-sectional shape of the beam.
The micro-optically active structures are easily producible, for example, by means of electron beam lithography, photolithography or ion exchange methods.
In a development of the invention, a device for beam focusing is arranged in front of and behind the micro-optically structured surface. The size of the beam cross section can be adjusted with this device. For example, a collective lens can be provided as a device of this kind which is positioned in the beam path in front of or after the structured surface.
Preferably, zoom optics can be provided as a device for beam focusing; with zoom optics it is possible to influence the size of the spot in a simple manner. When the zoom optics are coupled with corresponding automatic adjustment means, the spot size can be changed during treatment in an uncomplicated manner.
In another construction of the invention, the optical element with the micro-optically active surface is constructed as a beam-guiding rod in which the beam is relayed by total reflection. The rod has an input radiation surface and an emission surface for the laser beam; the input radiation surface is provided with the micro-optically active structure. The rod can be made of silica glass. The size and cross-sectional shape can differ between the in-radiation surface and out-radiation surface. Advantageously, however, the in-radiation surface should be round, the round cross section should be retained over at least 90% of the length of the rod, and a reduction and/or change in the shape of the cross section should be provided only in the remaining length.
Because of the total reflection within the beam-guiding rod, a further xe2x80x9cblendingxe2x80x9d of the plurality of individual partial beams present after passing through the structured surface is achieved and the beam intensity is made more uniform with respect to the beam cross section.
It should be noted that the micro-optic structures, insofar as they are formed on the in-radiation surface of a beam-guiding rod as provided according to the invention, can also be the structures of a diffusion plate or scatter disk known from the prior art. However, since the light also enters at an unfavorable angle with the indefinable structures of the scatter disk, the back reflections would result in energy losses and accordingly also in undesirably excessive heat development.
This is prevented by the micro-optically active structures because they are constructed in such a way that unfavorable entrance angles do not occur. In this case, in accordance with the Fresnel equations (relationship between polarization, reflection, absorption), approximately 96% of the laser radiation is coupled in, so that the energy loss and accordingly also the heat development is limited to a reasonable amount.
An additional influencing of the beam intensity distributed over the cross section can be achieved when the structured surface is curved, preferably in concave manner, but particularly preferably also in convex manner.
The emission surface can have a circular as well as a polygonal, e.g., square or hexagonal, cross section.
Further constructions in which a ruby laser or a laser diode integrated in the handpiece is provided as laser radiation source lie within the scope of the invention.
Further, a layer of transparent gel, for example, an ultrasound gel, can be provided between the emission surface and the skin surface to be treated. The radiating of the laser beam into the skin surface to be treated is further optimized in this way by reducing the reflection and decreasing scatter. As a further result, lower energy densities are needed for the laser light. The refractive index of the gel is to be adapted to the refractive index of the skin and the gel should be transparent at least for the wavelength of the utilized laser light.
The invention is further directed to a method for cosmetic treatment of skin surfaces while operating a handpiece corresponding to the preceding description. According to the invention, a first contact surface is initially placed on a selected skin area to be treated for purposes of moderating temperature. After a predetermined holding time during which this first contact surface is held on the skin area, the position of the handpiece is changed in such a way that the laser radiation emission surface, and not the contact surface, is located over this skin area. The contact surface is already in heat-conducting contact with another skin area to be treated which is located directly adjacent to the first skin area. During the period in which the contact surface is held on the second skin area, the treatment of the first skin area with the laser beam is carried out.
After the treatment is concluded, after which pre-cooling of the second skin area is also concluded, the position of the handpiece is changed in such a way that the exit surface for the laser beam is now located over the second skin area and the contact surface is in heat-conducting contact with a third skin area and effects a preliminary moderation of the temperature of the latter. During this holding time, the second skin area undergoes treatment with the laser radiation.
Alternatively, the change in the position of the handpiece from one treated skin area to the next can be carried out by shifting, wherein the handpiece is applied, the radiation source is switched on for the treatment period specifically for this skin area and is then switched off again, or by moving in a sliding manner over the skin areas to be treated, while the laser beam remains switched on.
In the latter case, the laser energy, the cooling temperature at the contact surface for pre-cooling, the temperature at the contact surface for subsequent temperature moderation (if any) and the forward feed speed of the handpiece are adapted to one another in such a way that treatment is carried out in an optimal manner. A plurality of xe2x80x9cpathsxe2x80x9d of this kind can be carried out side by side to treat a larger skin surface.
In a further development of this method for cosmetic treatment of skin surfaces using the handpiece described above, a gel is applied to the skin surface to be treated before the treatment is started, wherein the gel is transparent for the wavelength of the utilized laser light and its index of refraction is adapted to the index of refraction of the skin. In this way, laser energy is effectively applied to the skin because the light reflected by the skin is reduced to an insignificant proportion. This prevents secondary effects which would otherwise occur due to lost heat.
An ultrasound gel whose index of refraction lies between that of the emission surface and that of the skin surface to be treated is preferably used. The ultrasound gel is physiologically tolerated and therefore suitable for cosmetic purposes. Moreover, it has good heat conductivity.
The gel further reduces the risk of damaging the epidermis. The efficacy of the gel can be further increased by removing any hair from the part of the skin to be treated before beginning the treatment.